442 
perfect insect, which support the three 
first rings of the trunk. In many larve 
there are no organs of locomotion, whilst 
others are furnished with a variable num- 
berof rudimental legs, presenting differently 
constituted organs for progression. Most 
of the larve of the Lepidoptera have ten 
MOTION. 
pair of these pro-legs, respectively arti - 
culated to the sixth, seventh, eighth, ninth, 
and anal segments of the body. One 
family, the Lophyrus, has sixteen pro-legs. 
Others, as the Stylotoma, have fourteen, 
and the Tenthredo twelve. The perfect legs 
move (according to Kirby and Spence) in the 
same order as in the imago state; the pro- 
legs serve not only to raise and support the 
abdominal and caudal segments of the trunk, 
but also to assist in grasping objects in the 
plane of motion, and in urging the centre of 
gravity forwards. 
When the head and thoracie segments are 
fixed, the body and tail are drawn forwards ; 
the trunk is arched in the vertical plane; the 
tail being fixed, the pro-legs are advanced 
successively in pairs, beginning from the anal 
segment; the body is then extended, and 
the head advanced to take a new position; a 
conspicuous undulation of the body is produced, 
proceeding from the caudal to the cephalic seg- 
ments. The larva of the Ant-lion (Myrmeleon) 
moves in a backward direction, even after the 
removal of its legs. Many larve, such as the 
Caterpillar of the Hawk-moth, move with ex- 
treme slowness, whilst others possess consi- 
derable powers of locomotion, as the Apotela 
Leporina, which has received its appellation 
from the rapidity of its movements. But of all 
terrestrial larvee, the most remarkable for their 
attitudes and motions are the Geometre. The 
true Geometre have only two anal, and two in- 
termediate pro-legs ; with these they grasp any 
object so as to fix the anal extremity : the trunk, 
with the head, is then extended, elevated, and 
inclined from the horizontal towards the vertical 
position, and the animal appears to be in the 
act of surveying surrounding objects as repre- 
sented in fig. 233. In progression,thehead being 
Fig. 233. 
a4 
fixed on the surface of motion at ¢ (fig. 234) ; 
the anal extremity is drawn forwards to the 
thoracic segments, from a to b; the trunk is 
then again extended to d, and a series of the 
same alternate flexions and extensions is em- 
ployed to carry the larva onwards. During 
progression, the Geometre spin a silken cord, 
which they fix by the head on the plane of 
position at each step, thus measuring the dis- 
tance over which they pass. The use of this 
cord is to enable them to descend from the 
trees, however lofty, on which they feed, and 
to reascend by the same means, without th 
necessity of taking a circuitous route, an 
encountering the inequalities of the trunk am 
branches. In like manner the Caterpillars ©: 
the Cabbage-butterfly weave a ladder of silk 
on the plane of a glass-window, which serves 
as a fulcrum for its legs, and thus enables the 
animal to ascend. -*5 
Perfect Insects—The order in which the 
of the Hexapods move in walking or ranning has 
been accurately explained by Professor Muller. 
Whilst watching insects which move slowly, 
he observed that three of their legs were always 
moving at the same time; these were advance 
and put to the ground, whilst the other three 
ropelled the body of the insect forwards. 
The feet, which moved simultaneously, wei 
the fore and hindmost foot on one side, an 
the middle foot of the opposite side; the 
the fore and hind foot on this side, and th 
middle one of the other side, so that in two step 
all the six feet are set in motion.* In the 
movement, whilst the legs, 1, 2‘, 3, (fig. 
fom 
oy 
a 
A , 
Fig. 235. 
1 v r 
2 2’ 
8 3’ 
4 
™ 
= 
remain on some solid to support the body, 
project it forwards, the Ocha three le 
1,’ 2, 3, are raised and advanced ; then, wh 
the legs, 1’, 2, 3’ are, in their turn, support 
the body, 1, 2’, 3 are raised and advanced, ¢ 
so on alternately. It will be observed, 
the base of support in these movements i 
triangular plane, with the three feet p 
the three angles; the base and apex ol 
triangle alternating at each alternate moven 
of each set of legs; so that in the first m 
ment, the apex, which is at 2, takes the o 
re side at 2’ in the second step. The H 
s are supported by their three pairs of 
and the stability of the animal is z 
the horizontal direction of the legs ot 
this arrangement affording a larger tal 
support of the centre of gravity. Th 
pair of legs being articulated to the proth 
the second pair to the mesothorax, 
third to the metathorax, also gives to th 
axis an increased stability. The articul 
: 
* Miiller, by Dr. Baly, p, 970. 
oa 
ve 
